1. Field of the Invention
The amount of nitrogen oxides (hereinafter referred to as NOx) which forms as gaseous or liquid fuels burn in various industrial furnaces or boilers depends on conditions for combustion, especially such factors as the flame temperature, oxygen concentration and residence time of the burnt gases in the high temperature region; the higher the flame temperature and the higher the oxygen concentration, the larger the amount of NOx.
2. Description of the Prior Art
It has been a common practice for combustion in general to ensure the uniform mixing of combustion air and fuel as early as possible to effect quick combustion, from the standpoint of increasing combustion efficiency. Such quick combustion, however, elevates the flame temperature, enlarges the high temperature region in the furnace and increases the localized oxygen concentration in the combustion zone, with the consequent result of the formation of a large amount of NOx. Hence an incompatibility between desires for maximum combustion efficiency and a minimum of environmental pollution.